The present invention relates to optical technology, and more particularly to a method and system for splitting or combining an optical signal.
Conventional optical signals are often desired to be split or combined based on the polarization of the signal. In order to perform either of these functions, a conventional splitter/combiner is often used. FIG. 1 depicts a conventional splitter/combiner 10. The conventional splitter/combiner 10 includes fiber 12 at one end and fibers 36 and 46 at the opposite end. The fibers 36 and 46 are polarization-maintaining fibers. Consequently, an optical signal travelling over one of the fibers 36 and 46 will maintain its polarization. The conventional splitter/combiner 10 includes collimators 13, 30 and 40 for collimating the optical signals carried on fibers 12, 36 and 46, respectively. Each conventional collimator 13, 30 and 40 typically includes a capillary 14, 34 and 44, respectively. The capillaries 14, 34 and 44 hold each fiber 12, 36 and 46, respectively. The collimators 13, 30 and 40 also include lenses 16, 32 and 42, respectively. The lenses 16, 32 and 42 are used in conjunction with the capillaries 14, 16 and 44, respectively, for collimating the optical signals carried on fibers 12, 36 and 46, respectively.
The conventional splitter/combiner 10 also includes a large birefringent crystal 20. A birefringent crystal has the property that light polarized in one direction (xe2x80x9cordinary signalxe2x80x9d) is deflected based on a different index of refraction than light polarized in a second, perpendicular direction (xe2x80x9cextraordinary signalxe2x80x9d). Any unpolarized optical signal can represented by an optical signal polarized in two perpendicular directions. Here, the optical signal can be decomposed into two portions polarized in the plane of the page and out of the plane of the page. The birefringent crystal 20 is oriented so that one portion of the optical signal polarized in out of the plane of the page and perpendicular to the optic axis 21 (xe2x80x9cconventional ordinary signalxe2x80x9d) is transmitted undeflected. The birefringent crystal 20 also deflects a remaining portion of the optical signal polarized in another direction (xe2x80x9cconventional extraordinary signalxe2x80x9d). FIG. 1 depicts the conventional ordinary signal 24 and the conventional extraordinary signal 22 traveling through the birefringent crystal 20. As depicted in FIG. 1, the ordinary signal is polarized in a direction perpendicular to the optic axis 21 of the birefringent crystal 20. Furthermore, as depicted in FIG. 1, the optical signal enters the birefringent crystal 20 in a direction perpendicular to the face of the birefringent crystal 20. Thus, the angle of incidence of the optical signal, measured from a direction perpendicular to the face of the birefringent crystal 20, is zero degrees.
The conventional splitter/combiner 10 splits the optical signal input at the fiber 12 into two signals, based on the polarization of the signals. The signal from the input fiber 12 is collimated by the collimator 13 and transmitted to the birefringent crystal 20. The birefringent crystal 20 splits the input signal to the conventional ordinary signal 24 and the conventional extraordinary signal 22. Because of the orientation of the birefringent crystal 20 with respect to the collimator 13 and the direction of the optic axis 21, the conventional extraordinary signal 22 is transmitted at an angle, while the conventional ordinary signal 24 is transmitted undeflected. Thus, at the end of the birefringent crystal 20 closer to the fibers 36 and 46, the conventional ordinary signal 24 and the conventional extraordinary signal 22 are separated by a distance. The conventional ordinary signal 24 and the conventional extraordinary signal 22 are output from the birefringent crystal 20 in parallel. The conventional extraordinary signal 22 is provided to collimator 30 and output over polarization-maintaining fiber 36. Similarly, the conventional ordinary signal 24 is transmitted to the collimator 40 and output over the polarization-maintaining fiber 46.
When the conventional splitter/combiner 10 is to combine signals, the signals are input at fibers 36 and 46. The polarizations of the input signals provided over the fibers 36 and 46 are preferably that of the conventional extraordinary signal 22 and conventional ordinary signal 24, respectively. Because of the orientation of the birefringent crystal 20, the conventional extraordinary signal 22 and conventional ordinary signal 24 are combined. The combined signal is then transmitted to the collimator 13 and output via the fiber 12. Thus, the conventional splitter/combiner 10 can thus split or combine optical signals.
Although the conventional splitter/combiner 10 functions, one of ordinary skill in the art will readily recognize that the conventional splitter/combiner 10 is large and expensive. The birefringent crystal 10 is made large to develop a sufficient space between the conventional ordinary signal 24 and the conventional extraordinary signal 22. Furthermore, multiple collimators 13, 30 and 40 for the fibers 12, 36 and 46 consume space. The birefringent crystal is also costly due to its size. Furthermore, the number of components, such as the use of three collimators 13, 30 and 40 also add to the cost of the conventional splitter/combiner 10. The conventional splitter/combiner 10 is, therefore, large and expensive.
Accordingly, what is needed is a system and method for providing a splitter/combiner that is smaller and less expensive. The present invention addresses such a need.
The present invention provides a method and system for providing a splitter/combiner. The splitter/combiner comprises a first birefringent wedge having a first optic axis and a first wedge angle and a second birefringent wedge having a second optic axis and a second wedge angle. The second birefringent wedge is optically coupled with the first birefringent wedge. The second wedge angle is complementary to the first wedge angle. The second optic axis is perpendicular to the first optic axis such that an extraordinary signal for the first birefringent wedge is an ordinary signal for the second birefringent wedge. The first and second birefringent wedges establish a first path for a first portion of a first optical signal and establish a second path for a second portion of the first optical signal. The first path and the second path are separated by an angle. The first optical signal travels from the first birefringent wedge to the second birefringent wedge. The first birefringent wedge and the second birefringent wedge also combine a second optical signal travelling along the first path with a third optical signal travelling along the second path. The second optical signal and the third optical signal travel from the second birefringent wedge to the first birefringent wedge.
According to the system and method disclosed herein, the present invention provides a splitter/combiner which can be made smaller and more cheaply than conventional splitter/combiners.